1. Technical Field
The present invention relates to touch panels, electrooptical devices, and electronic apparatuses.
2. Related Art
A surface acoustic wave (SAW) touch panel includes transmitting transducers that transmit surface acoustic waves propagating the panel surface and receiving transducers that receive the surface acoustic waves. An obstacle on the SAW touch panel obstructs and absorbs the surface acoustic waves, which are received by the receiving transducers in a partially attenuated waveform.
The surface acoustic waves are absorbed when a user touches the SAW touch panel surface. The touch panel system measures the time that elapses before an attenuated waveform appears on the waveforms of the surface acoustic waves received by the receiving transducers. Based on the measurements, the touch panel system calculates the X and Y coordinates of a position touched by the user on the panel surface to detect the touched position. SAW touch panels are used as input devices attached on displays for various apparatuses such as word processors and automated teller machines (ATMs). In particular, the use of SAW touch panels as input devices attached on displays for mobile electronic apparatuses such as personal digital assistants (PDAs) and palmtop computers has recently been studied
Mobile electronic apparatuses experience frequent vibrations and impacts. Because panel surfaces of SAW touch panels are exposed, they are easily chipped and cracked by vibrations and impacts and undesirably scatter glass shards A known type of SAW touch panel has a protective film on a panel surface to protect the panel surface and prevent scattering of glass shards.
If, for example, the protective film is laminated on the panel surface with an adhesive, the adhesive absorbs the surface acoustic waves. If the protective film is simply placed on the panel surface, a malfunction can occur when they become misaligned. To solve this problem, for example, Japanese Patent No. 3,010,669 discloses an SAW touch panel having spacers between a panel body and a protective film to hold the panel body and the protective film.
In the structure disclosed in this publication, however, the spacers absorb the surface acoustic waves. The attenuation of the surface acoustic wave due to the spacers is difficult to distinguish from attenuation of the surface acoustic wave due to touching. The touch panel system therefore causes misdetection or malfunction and exhibits low position detection performance.